In the field of menstrual pads, an unacceptable failure rate still exists with most products currently in use. Most pads cannot effectively absorb the overall amount of menstrual fluid exuded; moreover, they cannot absorb the fluid at the high flow rate encountered at certain times. Additionally, the absorbed fluid tends to remain at the point of collection. Improved distribution of menstrual fluid across the surface of the pad would therefore be desirable and would result in increased absorption by utilizing the full absorptive capacity of the materials within the pads.
Traditionally, menstrual pads have been made from fabric, pulp, and/or synthetic fibers, such as polypropylene, polyethylene, polyester, and other fibers. More recently, new higher absorbency products have been incorporated into these pads. One such absorbent is comprised of a thin layer of processed, compressed peat moss, which is scored to improve liquid penetration and absorbency, as described in U.S. patent application Ser. No. 851,270 of Mar. 13, 1992, which is assigned to the assignee of the present invention. However, peat moss board, while extremely high in capacity, is slow to absorb fluid and, therefore, napkins using peat moss board as an abosrbent, require additional means to aid in absorption.
Superabsorbents have also been used to increase the amount of liquid which is absorbed and retained by absorbent personal products. For example sodium carboxymethylcellulose (CMC) commercially available as AQUASORB/AS50 from the Aqualon Company of Wilmington, Del., USA is frequently used in personal care applications for absorbing and retaining blood, saline or other body fluids. Superabsorbents typically absorb from 5 to 10 times their dry weight of water, although somewhat less by weight of menstrual fluid, which is absorbed at a relatively lower rate. While superabsorbents have certain advantages, they tend to form a gel as they absorb fluid. The gel prevents fluid from flowing deeper into the superabsorbent layer. This phenomenon is known as "gel-blocking". Gel-blocking occurs because as fluid encounters a quantity of superabsorbent, the first portion of the superabsorbent to contact the liquid being absorbed turns into a gel. Because superabsorbents tightly bind liquid once it has been absorbed, they cause other efficiency decreasing effects. As absorption occurs, the superabsorbent swells considerably; normally, superabsorbent powders are distributed within a fibrous matrix, such that the swelling is accommodated through a compression of the surrounding fibers. If the surrounding fibers are already near saturation, the swelling of the superabsorbent may not result in as much of an increase in absorptive capacity as would be expected. It is important, however, to overcome these phenomena and achieve maximum efficiencies when using superabsorbents, since they are more expensive on a per weight basis than any other component of a typical absorbent product.
Thus, a need still exists for a comfortable menstrual pad which rapidly absorbs fluid and retains that fluid for extended periods of time without leaking. It would therefore be desirable to be able to incorporate superabsorbents and/or the improved absorbent peat moss products described above into an absorbent pad while making maximum efficient use of the absorbent properties of those materials.